The study, published in Psychological Science, states, "Extremely positive experiences, and positive appraisals thereof, produce intense positive emotions that often generate both positive expressions (e.g., smiles) and expressions normatively reserved for negative emotions (e.g., tears). We developed a definition of these dimorphous expressions and tested the proposal that their function is to regulate emotions."

There are many examples of how one can react to a positive experience with a negative emotion. For instance, the emotional expressions people show in response to adorable babies. At the same time that adults are baby talking to babies and holding them, they also can't resist pinching their cheeks, squeezing them tight, and wanting to gnaw at them.

Dimorphous expressions — two different expressions that have the same origin — aren't situation specific; rather, they seem to emerge in response to a variety of good feelings.

"People may be restoring emotional equilibrium with these expressions," said Oriana Aragon, lead researcher of the study. "They seem to take place when people are overwhelmed with strong positive emotions, and people who do this seem to recover better from those strong emotions."

As part of the study, the researchers asked subjects to look at and evaluate photos of different babies, some who appeared more "babyish" (bigger eyes) than others. Participants demonstrated higher expressions of care for the more infantile babies, and said they wanted to take care of them and protect them. But they also reported high expressions of aggression in response to these babies, saying they wanted to "pinch their cheeks" and "eat them up."

The research indicated that it was specifically the feeling of being overwhelmed by positive emotion that evoked the aggressive responses.

People who showed higher expressions of aggression while looking at the babies tended to show a bigger drop-off in positive emotion five minutes after seeing the images, suggesting that the negative emotions helped the participants to neutralize their intense positive emotions, bringing them back to emotional equilibrium.

"These insights advance our understanding of how people express and control their emotions, which is importantly related to mental and physical health, the quality of relationships with others, and even how well people work together," Aragon said.

So the next time you want to squeeze that baby's face, know that you aren't some crazed baby-squeezer — just someone who's getting their emotional balance back.